/*
 * Copyright 2017 StreamSets Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.streamsets.pipeline.api.ext.io;

import java.io.FilterReader;
import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;

/**
 * Included from Apache commons
 *
 * A Proxy stream which acts as expected, that is it passes the method
 * calls on to the proxied stream and doesn't change which methods are
 * being called.
 * <p>
 * It is an alternative base class to FilterReader
 * to increase reusability, because FilterReader changes the
 * methods being called, such as read(char[]) to read(char[], int, int).
 *
 * @version $Id: ProxyReader.java 1304052 2012-03-22 20:55:29Z ggregory $
 */
public abstract class ProxyReader extends FilterReader {

  /**
   * Constructs a new ProxyReader.
   *
   * @param proxy  the Reader to delegate to
   */
  public ProxyReader(Reader proxy) {
    super(proxy);
    // the proxy is stored in a protected superclass variable named 'in'
  }

  /**
   * Invokes the delegate's <code>read()</code> method.
   * @return the character read or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public int read() throws IOException {
    try {
      beforeRead(1);
      int c = in.read();
      afterRead(c != -1 ? 1 : -1);
      return c;
    } catch (IOException e) {
      handleIOException(e);
      return -1;
    }
  }

  /**
   * Invokes the delegate's <code>read(char[])</code> method.
   * @param chr the buffer to read the characters into
   * @return the number of characters read or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public int read(char[] chr) throws IOException {
    try {
      beforeRead(chr != null ? chr.length : 0);
      int n = in.read(chr);
      afterRead(n);
      return n;
    } catch (IOException e) {
      handleIOException(e);
      return -1;
    }
  }

  /**
   * Invokes the delegate's <code>read(char[], int, int)</code> method.
   * @param chr the buffer to read the characters into
   * @param st The start offset
   * @param len The number of bytes to read
   * @return the number of characters read or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public int read(char[] chr, int st, int len) throws IOException {
    try {
      beforeRead(len);
      int n = in.read(chr, st, len);
      afterRead(n);
      return n;
    } catch (IOException e) {
      handleIOException(e);
      return -1;
    }
  }

  /**
   * Invokes the delegate's <code>read(CharBuffer)</code> method.
   * @param target the char buffer to read the characters into
   * @return the number of characters read or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   * @since 2.0
   */
  @Override
  public int read(CharBuffer target) throws IOException {
    try {
      beforeRead(target != null ? target.length() : 0);
      int n = in.read(target);
      afterRead(n);
      return n;
    } catch (IOException e) {
      handleIOException(e);
      return -1;
    }
  }

  /**
   * Invokes the delegate's <code>skip(long)</code> method.
   * @param ln the number of bytes to skip
   * @return the number of bytes to skipped or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public long skip(long ln) throws IOException {
    try {
      return in.skip(ln);
    } catch (IOException e) {
      handleIOException(e);
      return 0;
    }
  }

  /**
   * Invokes the delegate's <code>ready()</code> method.
   * @return true if the stream is ready to be read
   * @throws IOException if an I/O error occurs
   */
  @Override
  public boolean ready() throws IOException {
    try {
      return in.ready();
    } catch (IOException e) {
      handleIOException(e);
      return false;
    }
  }

  /**
   * Invokes the delegate's <code>close()</code> method.
   * @throws IOException if an I/O error occurs
   */
  @Override
  public void close() throws IOException {
    try {
      in.close();
    } catch (IOException e) {
      handleIOException(e);
    }
  }

  /**
   * Invokes the delegate's <code>mark(int)</code> method.
   * @param idx read ahead limit
   * @throws IOException if an I/O error occurs
   */
  @Override
  public synchronized void mark(int idx) throws IOException {
    try {
      in.mark(idx);
    } catch (IOException e) {
      handleIOException(e);
    }
  }

  /**
   * Invokes the delegate's <code>reset()</code> method.
   * @throws IOException if an I/O error occurs
   */
  @Override
  public synchronized void reset() throws IOException {
    try {
      in.reset();
    } catch (IOException e) {
      handleIOException(e);
    }
  }

  /**
   * Invokes the delegate's <code>markSupported()</code> method.
   * @return true if mark is supported, otherwise false
   */
  @Override
  public boolean markSupported() {
    return in.markSupported();
  }

  /**
   * Invoked by the read methods before the call is proxied. The number
   * of chars that the caller wanted to read (1 for the {@link #read()}
   * method, buffer length for {@link #read(char[])}, etc.) is given as
   * an argument.
   * <p>
   * Subclasses can override this method to add common pre-processing
   * functionality without having to override all the read methods.
   * The default implementation does nothing.
   * <p>
   * Note this method is <em>not</em> called from {@link #skip(long)} or
   * {@link #reset()}. You need to explicitly override those methods if
   * you want to add pre-processing steps also to them.
   *
   * @since 2.0
   * @param n number of chars that the caller asked to be read
   * @throws IOException if the pre-processing fails
   */
  protected void beforeRead(int n) throws IOException {
  }

  /**
   * Invoked by the read methods after the proxied call has returned
   * successfully. The number of chars returned to the caller (or -1 if
   * the end of stream was reached) is given as an argument.
   * <p>
   * Subclasses can override this method to add common post-processing
   * functionality without having to override all the read methods.
   * The default implementation does nothing.
   * <p>
   * Note this method is <em>not</em> called from {@link #skip(long)} or
   * {@link #reset()}. You need to explicitly override those methods if
   * you want to add post-processing steps also to them.
   *
   * @since 2.0
   * @param n number of chars read, or -1 if the end of stream was reached
   * @throws IOException if the post-processing fails
   */
  protected void afterRead(int n) throws IOException {
  }

  /**
   * Handle any IOExceptions thrown.
   * <p>
   * This method provides a point to implement custom exception
   * handling. The default behaviour is to re-throw the exception.
   * @param e The IOException thrown
   * @throws IOException if an I/O error occurs
   * @since 2.0
   */
  protected void handleIOException(IOException e) throws IOException {
    throw e;
  }

}
